Today when using utility vehicles, such as a truck or a bus, there are some legislative demands that assist in reducing pollution. However, different engine types need different control parameters to optimize combustion. For instance a diesel-powered engine will need no system that detects misfiring, whereas an engine powered by alternative fuels will need such a system to optimize combustion. It is becoming more and more common to use engines powered by alternative fuels for utility vehicles and therefore also an increased need of systems that may detect other parameters than those needed to meet todays legislative demands for diesel engines, e.g. an increased need for detecting misfiring.
Detecting misfiring can be made in different ways. To meet this demand the control system of the vehicle has to be completed with a function for detecting misfiring. This can be both an expensive and an advanced procedure.
The document JP 2001050114 shows a method to detect misfiring in an engine powered by compressed natural gas. The method is founded on analysis of variables as rotational speed of the engine and a feedback of the air/fuel ratio. This is a typical example which will be both expensive and require an advanced procedure.
The document US 2008289600 shows a method for an engine to use two types of fuels with different octane numbers and ion current analysis is used to calculate the combustion timing such that the fuel mix to each cylinder may be adjusted from this calculation. The document also suggests that misfiring may be detected by a sensor signal from the rotational speed or by measurement of temperature and oxygen concentration in the exhausts through existing sensors in the engine. However, this method inherently comes with some disadvantages, e.g. that it is a complex system in need of a multiplicity of different sensors supplying a complex set of signals, i.a. leading to a risk for misinterpretation of combinations of the signals.
Many control system are known that use ion current sensing to detect different aspects and to control combustions parameters. From US 20030200023 (D2) and US 20030209211 (D3) there are known such a systems, which however do not present any solution how to also handle misfire detection in a reliable manner. U.S. Pat. No. 6,298,717 (D4) presents another system which suggests the use of a ion sensing in combination with revolution data, depending on operation conditions, implying a complex mode of functioning. “Kaiadi, M Diluted Operation of a Heavy-duty Natural Gas Engine. Aiming at Improved Efficiency, Emissions and Maximum Load. Doctoral thesis. Division of Combustion Engines. Department of Energy Sciences. Faculty of Engineering. Lund University. Doktorsavhandling. Januari 2011.” (D1) describes another known system using ion current sensing as one of many means to optimize combustion, but it does not provide any reliable solution regarding how to detect misfires using ion current in diluted SI-engines.